White roofs reflect up to 90% of sunlight (and the heat that comes with it) as compared to traditional black roofs that reflect only 20%.
What is a white roof?
A white roof is a lot more than just white paint! White roofs’ benefits are measured partly according to the solar reflectance index, or SRI. A roof’s SRI is a measure of a surface’s ability to reflect solar heat. SRI measures reflectance (reflecting the sun’s rays) and thermal emittance (the roof’s ability to radiate absorbed heat). If you’ve ever worn a black t-shirt in the sun then you already understand that black’s reflectance is negligible and its emittance is zero. A white roof’s reflectance is as high as 90% and its emittance is 100%.
White roofs keep buildings cool and reduce energy use.
The Urban Heat Island effect is a measurable increase in ambient urban air temperatures resulting primarily from the replacement of vegetation with buildings, black surfaces like roofs and roads and other heat-absorbing infrastructure. Cities are full of these heat trapping black surfaces.
5–10% of summer electricity is used to compensate for the Urban Heat Island effect. Americans spend about $40 billion annually to air condition buildings — one-sixth of all electricity generated in this country! White roofs can reduce summer energy use by 10–40%, saving money and preventing pollution. White roofs can reduce the total Urban Heat Island effect in an impacted city by 1° to 2° F – enough to lower peak energy demand, reducing the risk of brownouts and blackouts.
White roofs help curb climate change.
White roofs help curb climate change. “…replacing non-reflective, dark roofing materials with white ones … (every 1000 square feet) would result in an equivalent CO2 offset of 10 metric tons (about $250) annually”.
What about white roofs in winter?
Here in the northern part of the United States, you might think that a black roof would provide a winter heating benefit to building owners. However, there are several factors that make any potential heat gain relatively immaterial: The laws of physics dictate that hot air will always rise. Thus, any heat that is transferred to the interior of a building structure from the outside will remain at the top of the structure, providing minimal heat savings. In all parts of North America during winter, there are fewer hours of sunlight to affect energy costs. In fact, in some areas, there is a greater than a six-hour difference between peak-summer and peak-winter sunlight, meaning there is less sunlight available to contribute to a building’s potential warming. Plus, the angle of the sun is less direct, which also helps to minimize warming potential.
For more information on white roofs or to read the full article, visit White Roof Project.
Hankin Group has a sustainable focus in all projects. Our company has designed a Mariott Residence Inn with a white roof, and many other eco-friendly features, and is pursuing LEED certification for the building. The Mariott Residence Inn is under construction on Route 322 & Fellowship Rd within the Spring Valley Business Park in Glen Mills, PA and is scheduled to open in early 2017.
Click here to learn more about Hankin Group’s sustainability efforts.